Impacts of Air Cavities on Hygrothermal Performance of Retrofitted Timber Frame Assemblies in Six US Climates

Despite the growing interest in moisture behavior in buildings, building envelope designs rarely undergo assessment for hygrothermal control, especially when it comes to energy efficiency retrofits. Timber frame structures often incorporate a continuous air cavity that separates the exterior cladding from the wall sheathing. Indeed, using an air cavity increases thermal performance. To date, however, few studies have examined the impacts of air cavities on the hygrothermal performance in retrofitting projects. This study used WUFI Pro software to assess the influence of air cavities on the hygrothermal performance of existing building envelope components. We tested various ventilation rates for each wall assembly across six climates of the US. Findings show that adding an air cavity on the exterior side of the wall can reduce water accumulation during the simulation period. This element can prove especially beneficial in hot and humid climates since it increases dryness rates in the assembly.